1. Field of the Invention
This invention relates to a method for manufacturing a semiconductor substrate having a semiconductor layer, in which a semiconductor element is formed, on a supporting substrate with an insulating film interposed therebetween, and particularly to a method for manufacturing a semiconductor substrate having a patterned structure for a buried electrode below the semiconductor layer.
2. Description of the Related Art
As a semiconductor substrate provided with a semiconductor layer for forming a semiconductor element therein on a supporting substrate interposing an insulating film therebetween, there is for example a SOI (Silicon On Insulator) substrate. The SOI substrate is made by forming an oxide film as an insulating film on a silicon substrate serving as a supporting substrate and forming a monocrystalline silicon thin film on the oxide film. When this kind of semiconductor substrate is used, not only does it become unnecessary to provide a separate step for insulating the semiconductor layer from the substrate but also the insulation performance is good and it is possible to form semiconductor elements on the monocrystalline silicon thin film with a high density to make integrated circuits.
In a semiconductor substrate having this kind of SOI structure, to form an element such as a double gate MOSFET, the idea of forming on the lower face of the oxide film or in the oxide film a buried electrode pattern to constitute a back gate or interconnection pattern has been being considered. However, in a conventional semiconductor substrate having a pattern structure for a buried electrode of this kind, manufacturing technology for sharply increasing the film thickness uniformity of the SOI layer (the monocrystalline silicon thin film) and greatly enhancing the film thickness controllability of when this SOI layer is formed as an extremely thin film has not been completed, and the development of this kind of manufacturing technology has been being awaited.